A multitude of different types of water sprinkler are commercially known. Many of these include sprinkler heads and are adjustable in the sense that the arc through which the head oscillates can be varied. A difficulty with such sprinklers is the complexity of the mechanisms provided to cause the sprinkler head to move back and forth through a predetermined arc and to adjust the magnitude of the arc. Small water driven turbines which themselves drive the head via gear boxes are employed in some sprinklers. Others obtain their drive by causing the water being sprayed to impact on an arm which is mounted for oscillatory movement. By way of a type of escapement mechanism, oscillation of the arm advances the sprinkler head. when the arm encounters a trip mechanism, the position of which is adjustable, the direction of rotation reverses.
Water fed along the water mains to such sprinklers is not necessarily free of foreign particles. Furthermore, particles of soil can enter the sprinkler particularly when a lawn in which sprinklers of the `pop-up` type are embedded is being cut. The complex mechanisms of the prior sprinklers can readily be jammed by foreign matter, which means that the water then sprays in one direction only.